The present invention relates to a dielectric ceramic material. More particularly, the present invention relates to a dielectric ceramic material with properties suitable for use in applications such as UHF antennas where a proper combination of dielectric constant and loss factor is desirable.
Several different dielectric ceramic systems are of potential use in antennas for RF and Microwave Frequencies. The advantage of using dielectrics in microwave devices is size reduction of the antenna, which is due to the phenomenon that the length of electromagnetic wave in a medium is inversely proportional to square root of its dielectric constant (λ˜1/√K). The dielectric constant of most commercial microwave materials varies from ˜10 to 30-40 to 80-100 with maximal ten-fold size reduction of antenna or resonator being achieved in the latter case. Part of such materials are described in patents: U.S. Pat. No. 5,840,642 to Kim et al., U.S. Pat. No. 5,569,632 to Jung et al., KR20040051732, CN1519216, RU2167842; PCT published patent application WO9721642 to Suvorov et al.; JP3192606, JP3183657; U.S. Pat. No. 4,442,220 to Ouchi et al., all of which are herein incorporated by reference in their entirety.
However, even ten-fold size reduction is not sufficient for devices in the UHF domain (470 MHz to 870 MHz) where wavelength ranges from about 30 to 60 cm, which requires significant increase in dielectric constant of material. Materials with much higher dielectric constant (>1000) are based on ferroelectric systems, thus characterized by high dielectric losses and significant frequency dependence of properties at UHF. In order to form a viable UHF antenna a dielectric must have the correct combination of dielectric constant and loss factor to allow for the miniaturization of the antenna over the desired UHF frequency range 450 MHz to 900 MHz when combined with other components in the final antenna configuration. Dielectric ceramic with K in the range of 250 to 380, based on the Ag(Nb,Ta)O3 system is described in PCT published patent application WO9803446 to Valant et al., however these materials are very expensive, require oxygen atmosphere at sintering and exhibit relatively high dielectric losses at UHF.
What is needed is an improved dielectric material for use in UHF antennas and/or other applications.
Therefore, it is a primary object, feature, or advantage of the present invention to improve over the state of the art.
It is a further object, feature, or advantage of the present invention to provide an improved dielectric material suitable for use in UHF antennas.
A still further object, feature, or advantage of the present invention is to provide a ceramic dielectric material that does not require special atmosphere control during sintering.
Another object, feature, or advantage of the present invention is to provide a ceramic dielectric material that does not use expensive metals such as silver, niobium or tantalum.
Yet another object, feature, or advantage of the present invention is to provide a ceramic dielectric material that has a relatively high dielectric constant and a low dielectric loss.
One or more of these and/or other objects, features, or advantages of the present invention will become apparent from the specification and claims that follow.